> OF COURSE I can do this in a loop. Or with a /e

Can you? I can, too:

perl -pe 's/cat/++$i/ge' file

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There's no special variable that counts matches. But there's one that's incremented with each line of input: $.. So if we could tell Perl that cat instead of a newline is the line delimiter... but of course we can do that! That's what $/ is for.

perl -pe 'BEGIN { $/ = "cat" } chomp; $_ .= $. unless eof' file

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Update: which can be rewritten to use substitution as you originally wanted: 

perl -pe 'BEGIN { $/ = "cat" } s{$/}{$.}' file

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map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: Perl substitute with the nth match by choroba
in thread Perl substitute with the nth match by misterperl

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